1. Field of the Invention
The present invention relates to an ultrasonic Doppler diagnostic apparatus, and more particularly, it relates to an ultrasonic Doppler diagnostic apparatus used to diagnose the function of a specimen on the basis of a change in velocity information over time within the specimen, and to a method of controlling the ultrasonic Doppler diagnostic apparatus.
2. Description of the Related Art
A coronary flow reserve is used as an index indicating the ability to increase a coronary blood flow in accordance with an increase in myocardial oxygen consumption, and is shown by a ratio of a coronary blood flow value at peak coronary dilatation to a coronary blood flow at rest. If the blockage of the blood flow is cancelled after a temporary blockage of the coronary blood flow, reactive hyperemia is shown in which coronary arterioles and capillaries distend at the maximum in response to ischemia. This ratio of the peak coronary blood flow during the reactive hyperemia to the coronary blood flow value at rest is referred to as the coronary flow reserve.
Recently, adenosine, dipyridamole, etc. have been used as coronary vasodepressors, and dobutamine, etc. have been used as sympathetic agonists, and the coronary flow reserve is evaluated from a ratio between coronary blood flow velocities before and after the load of these drugs. In the presence of coronary stenosis, peripheral coronary arteries are already distended at rest, so that a change in the coronary blood flow value is small even if the peripheral coronary arteries are maximally distended. Therefore, the coronary blood flow reserve is said to reflect the functional degree of coronary stenosis in coronary artery disease.
One of the representative methods of evaluating such a coronary flow reserve is, for example, an intravascular Doppler method as disclosed in Japanese Patent No. 2863624. However, this method is an invasive method and thus has many restrictions. Thus, transesophageal echocardiography is implemented as means for noninvasively evaluating the coronary flow reserve. Although this is a noninvasive method, the burden on a patient is too heavy. Further, owing to an improvement in the performance of ultrasonic diagnostic apparatuses, noninvasive transthoracic echocardiography has recently been the most popular method.
Here, there will be described a method of evaluating the coronary flow reserve using the transthoracic echocardiography.
First, an operator extracts a long axis view of left ventricle through apex cordis approach in a B mode, and then gradually rotates a probe counterclockwise, thus starting a scan so that right ventricle is reduced and the anterior interventricular groove is extracted. Then, the transition is made to a color mode. In the color mode, a left anterior descending coronary artery (LAD) appears and disappears outside the anterior myocardial epicardium in the vicinity of the apex of heart. Here, if the left anterior descending coronary artery (LAD) which is displayed in a warm color during diastole is confirmed, the transition is made to a pulse Doppler (PWD) mode, and a sample volume is applied to the blood flow therein to adjust the velocity of flow using in some cases an angle correction function.
Next, the operator saves a still image of the left anterior descending coronary artery before a drug load. Then, a drug is administered, and the operator continues an inspection (ultrasonic scan) while observing that there is no abnormality in the change of condition of the patient under the drug load. After several minutes, if the operator confirms a gradual increase in the velocity of blood flow in the left anterior descending coronary artery of the patient, the operator adjusts the velocity range and base line position of the apparatus accordingly.
Furthermore, still images are periodically saved to obtain information on the peak blood flow velocity during the diastole of the left anterior descending coronary artery under the drug load. Basically, the blood flow velocity in the left anterior descending coronary artery immediately after the drug load is not different from that before the drug load, but the value of the flow velocity gradually rises with time. Once the peak blood flow velocity is registered, the value of the flow velocity gradually drops with time. After several minutes, the condition returns to the same as before the drug load.
Meanwhile, time is not constant which passes before the peak blood flow velocity is registered in the left anterior descending coronary artery after the drug load. The reason is that the time varies depending on the build, constitution, physical condition and condition of the disease of a patient, and it is impossible under the present situation for the operator to know when the patient registers the peak blood flow velocity value.
Therefore, the operator needs to frequently repeat the operation of saving still images because a current velocity waveform of the left anterior descending coronary artery being displayed on the monitor of the ultrasonic diagnostic apparatus may be registering the peak flow velocity value of the patient after the drug load. Thus, the operator continues to periodically save still images until the time when the peak flow velocity value seems to be registered (until the time when a decrease in the flow velocity value can be recognized), and then the operator terminates the inspection.
Subsequently, a plurality of still images acquired during the inspection are read from the apparatus to start the preparation for carrying out the evaluation of the coronary flow reserve.
Then, an image before the drug load as shown in FIG. 1A (an LAD blood flow waveform a, an ECG waveform b) is read and selected from within the ultrasonic diagnostic apparatus, and a blood flow velocity value is found using a measurement function. Then, a plurality of images after the drug load as shown in FIG. 1B are read, and an image is selected from those images which seems to register the peak flow velocity value, and then the peak flow velocity value is found in the same manner using the measurement function.
Next, the coronary flow reserve is found from those two data as shown in FIGS. 1A and 1B. The value of the coronary flow reserve can be found by B/A, where A is the velocity before the drug load (at rest), and B is the velocity after the drug load (at the peak flow velocity).
In general, the blood flow velocity value before the drug load remains stable, and is therefore relatively easy to select and measure in many cases. However, since the flow velocity value changes with time in the blood flow waveform after the drug load, various velocity ranges and the base lines are often set, as shown in FIGS. 2A to 2D. Therefore, as shown in FIG. 3, so much time is required and the throughput of the diagnosis is decreased in order for the operator to accurately extract an image registering the peak flow velocity value from a plurality of (N) images.
As measures to improve such a situation, for example, Jpn. Pat. Appln. KOKAI Publication No. 2005-185731 has proposed an apparatus which founds shift amounts of the velocity range and the base line in image display and changes parameters by adjusting means for the velocity range and the base line.
There is also conceived a method which uses an automatic tracing function and an automatic measurement function when finding the peak blood flow velocities in the left anterior descending coronary artery before and after the drug load. However, in most cases, although the operator thinks that he/she has captured the left anterior descending coronary artery in accordance with a pulse Doppler method, extremely strong clutter signals c from heart walls, etc. are received as shown in FIG. 4 due to the displacement of the probe from the left anterior descending coronary artery or due to cardiac motion, so that the value of the peak blood flow velocity in the left anterior descending coronary artery can not be measured but the velocity of the clutter signal is measured.
Still another method is conceived which performs multi-review display, displays acquired still images at a time, and extracts one from those still images, in order to increase the throughput of extracting an image indicating the peak flow velocity value from the plurality of still images after the drug load. However, as shown in FIG. 5, a waveform obtained in accordance with the pulse Doppler method is displayed together with a cross-sectional image in a mode such as the B mode or color mode, so that an image indicating the waveform of the flow velocity is small as such. Therefore, it is often impossible to accurately select and extract the image indicating, for example, the peak flow velocity value.
As described above, according to prior art, when evaluating the coronary flow reserve by the transthoracic echo, the operator needs to carry out scanning while observing that there is no abnormality in the change of condition of the patient under the drug load, continue the observation of the blood flow velocity value while adjusting the setting of the flow velocity range of the apparatus and the setting of the base line position, and continue to periodically take images of blood flow waveforms until a peak velocity is registered. This has been a heavy burden both emotionally and physically.
Moreover, it is impossible to evaluate the coronary flow reserve in real time, and it is necessary, after an inspection (ultrasonic scan), to read data on a plurality of images taken during the inspection (ultrasonic scan), calculate a CFR value, and evaluate the coronary flow reserve, leading to so much time required for the diagnosis of the coronary flow reserve and to a low throughput.
Methods of measuring the flow velocity value necessary for the evaluation of the coronary flow reserve include, for example, (i) a method implemented using the automatic tracing function, and (ii) a method which visually selects an image corresponding to the peak flow velocity value from a plurality of images arranged in the multi-review display and detects a velocity using the measurement function. However, these methods have problems such as lack of reliability in the accuracy of measurement due to the influence of clutter, and much time spent on the measurement of the flow velocity due to complicated operation methods.